A sink drain with an improper trap is more common than you may think, especially on homes that are built on piers. A proper trap on a sink drain is required in order to prevent nasty toxic fumes from your sewage waste coming up through the pipes. A trap holds enough water to block the flow of gasses from the sewage. Without a proper trap, the gasses would come up through the pipes and into your home.
While these sewage gasses can be toxic to the occupants health, the most common problem would simply be the noxious odor. A properly installed plumbing trap is required, but unfortunately many plumbers have installed traps that have questionable performance. The most common culprit is the famous ‘S’ trap. Although these are very common and you can buy a complete ‘S’ trap plumbing kit at your local hardware store,
they have the potential to siphon the water out of the trap. With no water in the waste trap, sewage gasses are able to creep back up to the home.
Turning your improper ‘S’ traps into proper ‘P’ traps can be a costly repair and sometimes it is just not feasible. As home inspectors we are required to notify our clients to the presence of the improper ‘S’ traps. In many cases ‘S’ traps do not cause any major problems for the home occupants. In order for the ‘S’ trap to siphon the water out, a large amount of water is flushed down the drain at once. If you run a little more water down the sink drain, the trap should stay full and block the gasses like normal.